I can hear the frustration in your post.
I know where you are coming from. I get so tired of being told that if I do z, y, or z that I'll lose weight. I've tried x, y, z and the rest of the alphabet!
I think in
rare instances, some people gain weight even though they are eating healthy and exercises. There are
medical reasons this can happen. Again, it's very rare but very real. It could be a thyroid issue, it could be something rare like Cushings, or (in your case) the introduction of steroids causing trouble.
I think your best move would be to work with a doctor. Get the advice of a professional. If there is something going on medically, it isn't as simple as just cutting calories and exercising more. Clearly, it isn't working and if something is going on it may never work (at least not entirely).
Of course, yes, diet and exercise are important and necessary to lose weight. But you already knew that, right?
But if you are fighting against a condition, or fighting against the effect of these steroids, you may need to do MORE than just diet and exercise. So my advice, for whatever it's worth, is to keep up the healthy eating and exercise plan AND work with a doctor to figure out what is going on to cause your recent weight gain and the difficulty you've had in losing it.
Please don't waste anytime feeling guilty or embarrassed or beating yourself up. Gaining that much weight in such a short time absolutely 100% warrants a visit with your doctor. There is
something else going on (probably the steroids, maybe something else too) and it should be a addressed by your doctor.
Hang in there! You're doing great with the healthy eating, now you've just got to figure out how to get your body to respond to it!!